The present invention relates to a motion control device of vehicles, such as an automobile, and particularly, to a motion control device which controls the motion of a vehicle at the time of turning manipulation.
Conventionally, a motion control device including a braking force control device which controls a vehicle braking force so that an actual turning control variable becomes a target turning control variable is widely known as a kind of motion control device which controls the motion of a vehicle at the time of turning manipulation. In this braking force control device for vehicle stabilization control, at the time of turning manipulation of a vehicle, braking forces applied to right and left steered wheels are individually controlled so as to minimize, for example, the deviation of an actual yaw rate based on an actual steering state of the steered wheels from a target yaw rate based on the steering angle and steering speed of the steered wheels by a driver. For example, for vehicle stabilization control, a system referred to as a so-called dynamic stability control (hereinafter refer to as “DSC”) system which is adapted to perform the automatic control of a wheel braking force or the automatic control of engine output in addition to this is also a kind of such a braking force control system.
Additionally, in recent years, in addition to this braking force control, a steering angle control device which controls the steering angle of the steered wheels so that an actual turning control variable becomes a target turning control variable with respect to the steering angle control of the steered wheels is also put to practical use. In such a steering angle control device, the steering angle of the steered wheels is controlled so as to minimize, for example, the deviation of the actual yaw rate from the target yaw rate at the time of turning manipulation of a vehicle, and thereby, the steering of a driver is assisted. For example, a so-called steering stability control (hereinafter refer to as “SSC”) system is also a kind of steering angle control system.
Furthermore, a steering angle control device, including a steering assist control function at the time of split μ which performs the steering assist control of eliminating the unstable behavior of the vehicle caused by this split μ in a case where so-called split μ that a difference above a predetermined value exists in the value of a road surface friction coefficient (road surface μ) has occurred in the right and left wheels during vehicle traveling, is known as the steering angle control device.
In this steering assist control at the time of split μ, or the SSC control, in a case where unstable behavior has occurred in the vehicle, in order to eliminate this unstable behavior, there is, for example, a case where so-called counter steering compensation, which turns tires in an opposite direction instantly, etc., is performed.
It is usual to minimize any deviation, which cannot be eliminated only by automatic control of a steering angle, first, by automatically controlling the steering angle of steered wheels so that an actual turning control variable becomes a target turning control variable by the steering angle control in a case where the motion control of a vehicle at the time of turning manipulation is performed by combining the above-described steering angle control with the aforementioned braking force control, and by using the braking force control system concurrently and automatically controlling the braking force to each wheel in a case where the deviation (for example, yaw rate deviation) of the actual turning control variable from the target turning control variable exceeds the operation limit of the steering angle control system (for example, refer to JP-A-3-227762).
Meanwhile, as one of concrete control mechanisms for suitably assisting a driver in the steering wheel manipulation by the driver, a so-called variable gear ratio (hereinafter refer to as “VGR”) mechanism which enables a gear ratio corresponding to the steering angle (tire angle) of the steered wheels to a steering wheel steering angle to be changed is conventionally widely known. By including the VGR mechanism, the ratio of the steering angle of the steered wheels to the steering wheel steering angle can be made variable according to a vehicle speed, and the degree of a change in the steering angle of the steered wheels in a case where the steering wheel manipulation by the driver has occurred can be adjusted. For example, the small turn performance of a vehicle when entering a garage, etc. can be enhanced by turning the vehicle relatively greatly with a small amount of steering wheel manipulation at the time of ultra-low speed as when the vehicle enters a garage, while safety at the time of high-speed traveling can be improved by making a change in the tire angle small so that the traveling direction of the vehicle does not change over-sensitively with a slight amount of steering wheel manipulation.
Additionally, as another concrete control mechanism for suitably assisting a driver in steering wheel manipulation by the drive; in a case where there is steering wheel manipulation by the driver, a so-called compliance compensation (hereinafter refer to as “CmpC”) mechanism which advances the phase of a tire angle according to a steering speed (angle) is well-known. By including this CmpC mechanism, the tire can be turned instantly quickly according to the steering speed at the time of steering wheel manipulation, and the responsiveness of vehicle behavior to the steering wheel manipulation of the driver can be enhanced.
By using the CmpC mechanism and the VGR mechanism together, the steering wheel manipulation of the driver can be more effectively assisted.
FIG. 22 is a schematic diagram showing a driver steering angle (refer to a solid line curve L1) when steering wheel manipulation by the driver has occurred, and the request tire angle of the VGR mechanism (a VGR request tire angle: refer to a broken line curve L2) in a superimposed manner on a time axis. The VGR request tire angle is expressed by a waveform obtained by multiplying a driver steering angle by a gain (gear ratio) according to a vehicle speed. The VGR mechanism makes this gain variable according to a vehicle speed.
Generally, this VGR request tire angle is highly correspondent to a driver steering angle, but it is lowly correspondent to the behavior of the vehicle which has responded to a steering wheel manipulation. In addition, in this FIG. 22 and FIGS. 23 to 25 (which will be described later), all of the respective tire angles are shown in terms of a pinion angle.
Additionally, FIG. 23 is a schematic diagram showing a [VGR+CmpC] request tire angle (refer to one-dot chain line curve L3) obtained by further superimposing the request tire angle (CmpC request tire angle) of the CmpC mechanism on the VGR request tire angle (refer to the broken line curve L2) shown in FIG. 22 when the phase of the VGR request tire angle is advanced by the CmpC mechanism. The CmpC request tire angle is expressed by a waveform (which is shifted to the left by a predetermined amount in FIG. 23) whose phase has been advanced according to a steering speed at the time of steering wheel manipulation with respect to the VGR request tire angle.
Generally, this [VGR+CmpC] request tire angle is highly correspondent to a driver steering angle, and it is also highly correspondent to the behavior of the vehicle which has responded to a steering wheel manipulation.
Moreover, FIG. 24 is a schematic diagram showing a [VGR+CmpC+SSC] request tire angle (refer to a broken line curve L4) serving as a final request tire angle obtained by superimposing a request tire angle (SSC request tire angle) based on the steering angle control by the aforementioned SSC system, on the [VGR+CmpC] request tire angle shown in FIG. 23. As mentioned above, in a case where unstable behavior has occurred in the vehicle in the steering assist control at the time of split μ and the SCC control, so-called counter steering compensation is performed as steering assist control of eliminating this unstable behavior. For this reason, as shown by a region M of the broken line curve L4 of FIG. 24, discontinuity appears in a change in the [VGR+CmpC+SSC] request tire angle.
Accordingly, this [VGR+CmpC+SSC] request tire angle is highly correspondent to the behavior of the vehicle which has responded to a steering wheel manipulation, but it is lowly correspondent to a driver steering angle
As described above, in the motion control device which performs the motion control of a vehicle at the time of turning manipulation by combining the steering angle control and the braking force control, in a case where so-called oversteering has occurred at the time of turning manipulation, in order to eliminate or suppress the oversteering, the motion control device assists the steering of the driver by only the steering angle control by the steering angle controller when the behavior of the vehicle falls within a range from a normal region to a region where the compensation amount of the yaw moment is relatively small. When the yaw rate deviation becomes large with the progress of the oversteering, and the behavior of the vehicle falls within a limit region which exceeds the operation limit of the steering angle control system, the braking force control by the braking force controller is started. However, when the braking force control is started, a steering angle signal of the steering angle controller which has been continuing control until then is used.
However, there is a plurality of kinds of steering angle signals as described above (refer to FIGS. 22 to 24), and it is very important whether a certain steering angle signal is used in order to realize suitable braking force control and achieve rapid stabilization of vehicle behavior.